Pull Request resolves #24019
Also replaces this incomplete PR #47672

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

The calendar keyboard navigation has been updated to provide consistent keyboard behaviour for both the calendar and its time controls. It has never been accessible for a keyboard user.
It was impossible for a keyboard user to do anything other than change the date.
They could never reach the time fields or the button.
If it was an empty date field then they couldnt use the picker at all as you couldnt select a day with the keyboard and you couldnt reach the buttons with the keyboard

This PR has taken me a while as I have had to learn the js and find a mentor to support me in writing it but the PBF was a good opportunity to complete it but I believe it addresses all keyboard navigation issues with the calendar

This follows accessibility practice of "is it better than yesterday? Not is it perfect"

Testing Instructions

The changes to test:

• Calendar arrow keys now move the selected date and update the main calendar input.
• Pressing Enter after navigating with the arrow keys selects the currently highlighted date.
• The hours and minutes <select> controls now handle their arrow keys natively
• Up/Down changes the selected hour or minute without changing the date in the input.
• Left/Right in the time fields no longer changes the calendar date.
• Changes made through the time controls continue to update the main calendar input.
• Forward Tab navigation now moves from the calendar into the time controls:
  Calendar → Hours → Minutes → Clear → Today → Close → next field
• Reverse Shift+Tab navigation works correctly:
  Close → Today → Clear → Minutes → Hours → Calendar
• Leaving the calendar with Tab or Shift+Tab closes the calendar popup when focus moves outside the calendar field.
• Keyboard handling now uses keydown rather than keypress and keydown.
• RTL keyboard navigation has been tested, including the interaction between RTL calendar navigation and the time control

Please test with a calendar field that has a date value already and one that doesnt
eg for a saved article the Start Publishing already has a value and the Finish Publishing is empty

Sample keyboard navigation route

Go to Content/Article/New or Edit / Publishing tab
Use Tab key to move focus to calendar field
Use Tab key to move focus to calendar button
Ue space or enter key to open calendar
Use Left/Right/Down/Up arrows to select date
Use Tab key or Shift + Tab key to move focus to hours/minutes and then Clear/Today/Close buttons
Use Space/Enter key to place selected date into field and close the popup

This is a js change so you will need to either npm run build:js or use a prebuilt package to test

Actual result BEFORE applying this Pull Request

Expected result AFTER applying this Pull Request

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed